Browsing by Author "Moore, A."
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Item Open Access CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration(Elsevier, 2022-03-16) Bavarella, S.; Luqmani, Ben; Thomas, Navya; Brookes, Adam; Moore, A.; Vale, P.; Pidou, Marc; McAdam, Ewan J.Solids formation can substanitally reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Under conditions comparable to existing literature, NH4HCO3 was evidenced to primarily crystallise in the gas-phase (lumen-side of the membrane) due to the high vapour pressure of ammonia, which promotes gaseous transmission from the solvent. Investigation of solvent reactivity demonstrated how equilibria dependent reactions controlled the onset of NH4HCO3 nucleation in the solvent, and limited ‘slip’ through transfomation of ammonia into its protonated form which occurs prior to the phase change. Crystallisation in the solvent was also dependent upon ammonia concentration, where sufficient supersaturation must develop to overcome the activation energy for nucleation. However, this has to be complemented with a reduction in solvent temperature to offset vapour pressure and limit the risk of gas-phase crystallisation. While changes to the solvent chemistry were sufficient to shift from gas-phase to liquid phase crystallisation, wetting was observed immediately after nucleation in the solvent. This was explained by a local region of supersaturation within the coarse membrane pores that promoted a high nucleation rate, altering the material contact angle of the membrane sufficient for solvent to breakthrough into the gas phase. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS.Item Open Access A comparison of three modelling approaches for quantitative risk assessment using the case study of Salmonella spp. in poultry meat.(Elsevier Science B.V., Amsterdam., 2005-01-15T00:00:00Z) Parsons, David J.; Orton, T. G.; D'Souza J.; Moore, A.; Jones, R.; Dodd, C. E. R.A comprehensive review of both the scientific literature and industry practices was undertaken to identify and quantify all sources of contamination throughout the entire poultry meat production chain by Salmonella spp. This information was used to develop a quantitative risk assessment (QRA) model for Salmonella in the production chain from the breeder farm to the chilled carcass. This was subsequently used as the basis on which to compare the merits of three approaches to QRA modelling in such systems. The original model used a Bayesian Network (BN). The second method was a Markov chain Monte Carlo (MCMC) approach, a numerical Bayesian technique which retained a similar network structure but allowed further development, such as the separation of variability and uncertainty. The third method was a more detailed simulation model. The BN responds immediately to changes, such as entering evidence, because it does not use simulation and can propagate information from any point in the network to all others by Bayesian inference. However, it requires all the variables to be discrete, which introduces errors if continuous variables have to be discretized. These errors can accumulate. The MCMC approach does not require discrete variables while retaining some of the properties of the BN model, such as the ability to draw inferences from evidence. Finally, the simulation offers greater flexibility, such as consideration of the individual carcass, but may be more complex to implement as a result and sacrifices the ability to propagate evidence.Item Open Access Is chemically reactive membrane crystallisation faciliated by heterogeneous primary nucleation? Comparison with conventional gas-liquid crystallisation for ammonium bicarbonate precipitation in a CO2-NH3-H2O system(American Chemical Society, 2020-01-27) Bavarella, Salvatore; Hermassi, Mehrez; Brookes, Adam; Moore, A.; Vale, P.; Di Profio, G.; Curcio, E.; Hart, P.; Pidou, Marc; McAdam, EwanIn this study, membrane crystallisation is compared to conventional gas-liquid crystallisation for the precipitation of ammonium bicarbonate, to demonstrate the distinction in kinetic trajectory and illustrate the inherent advantage of phase separation introduced by the membrane to crystallising in gas-liquid systems. Through complete mixing of gas and liquid phases in conventional crystallisation, high particle numbers were confirmed at low levels of supersaturation. This was best described by secondary nucleation effects in analogy to mixed suspension mixed product removal (MSMPR) crystallisation, for which a decline in population density was observed with an increase in crystal size. In contrast, for membrane crystallisation, fewer nuclei were produced at an equivalent level of supersaturation. This supported growth of fewer, larger crystals which is preferred to simplify product recovery and limit occlusions. Whilst continued crystal growth was identified with the membrane, this was accompanied by an increase in nucleation rate which would indicate the segregation of heterogeneous primary nucleation from crystal growth, and was confirmed by experimental derivation of the interfacial energy for ammonium bicarbonate (σ, 6.6 mJ m-2), which is in agreement to that estimated for inorganic salts. The distinction in kinetic trajectory can be ascribed to the unique phase separation provided by the membrane which promotes a counter diffusional chemical reaction to develop, introducing a region of concentration adjacent to the membrane. The membrane also lowers the activation energy required to initiate nucleation in an unseeded solution. In conventional crystallisation, the high nucleation rate was due to the higher probability for collision, and the gas stripping of ammonia (around 40% loss) through direct contact between phases which lowered pH and increased bicarbonate availability for the earlier onset of nucleation. It is this high nucleation rate which has restricted the implementation of gas-liquid crystallisation in direct contact packed columns for carbon capture and storage. Importantly, this study evidences the significance of the membrane to governing crystallisation for gas-liquid chemical reactions through providing controlled phase separation.Item Open Access Recovery and concentration of ammonia from return liquor to promote enhanced CO2 absorption and simultaneous ammonium bicarbonate crystallisation during biogas upgrading in a hollow fibre membrane contactor(Elsevier, 2020-01-27) Bavarella, Salvatore; Hermassi, Mehrez; Brookes, Adam; Moore, A.; Vale, P.; Moon, I. S.; Pidou, Marc; McAdam, EwanIn this study, thermal desorption was developed to separate and concentrate ammonia from return liquor, for use as a chemical absorbent in biogas upgrading, providing process intensification and the production of crystalline ammonium bicarbonate as the final reaction product. Applying modest temperature (50°C) in thermal desorption suppressed water vapour pressure and increased selective transport for ammonia from return liquor (0.11MNH3) yielding a concentrated condensate (up to 1.7MNH3). Rectification was modelled through second-stage thermal processing, where higher initial ammonia concentration from the first stage increased mass transfer and delivered a saturated ammonia solution (6.4MNH3), which was sufficient to provide chemically enhanced CO2 separation and the simultaneous initiation of ammonium bicarbonate crystallisation, in a hollow fibre membrane contactor. Condensate recovered from return liquor exhibited a reduction in surface tension. We propose this is due to the stratification of surface active agents at the air-liquid interface during primary-stage thermal desorption which carried over into the condensate, ‘salting’ out CO2 and lowering the kinetic trajectory of absorption. However, crystal induction (the onset of nucleation) was comparable in both synthetic and thermally recovered condensates, indicating the thermodynamics of crystallisation to be unaffected by the recovered condensate. The membrane was evidenced to promote heterogeneous primary nucleation, and the reduction in the recovered condensate surface tension was shown to exacerbate nucleation rate, due to the reduction in activation energy. X-ray diffraction of the crystals formed, showed the product to be ammonium bicarbonate, demonstrating that thermal desorption eliminates cation competition (e.g. Ca2+) to guarantee the formation of the preferred crystalline reaction product. This study identifies an important synergy between thermal desorption and membrane contactor technology that delivers biogas upgrading, ammonia removal from wastewater and resource recovery in a complimentary process.Item Open Access The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors(Elsevier, 2023-08-02) Luqmani, Ben; Brookes, A.; Moore, A.; Vale, P.; Pidou, Marc; McAdam, EwanBiogas upgrading uniquely requires pressurisation of hollow fibre membrane contactors (HFMC) to be competitive with classical water absorption, and when complemented with an ambient industrial temperature range, these conditions will determine CO2 mass transport phenomena that are distinct dependent upon whether microporous or nonporous membranes are used. This study therefore examines the independent and concomitant role of temperature and pressure in determining CO2 mass transport, and selectivity, within microporous and nonporous HFMC. At low solvent temperatures, higher CO2 flux was achieved which indicates that solvent solubility is more critical than CO2 diffusivity to enhancing mass transport. Low temperatures also favoured mass transfer within the microporous membrane, explained by the reduction in solvent vapour pressure which limited pore wetting by condensation. In contrast, the nonporous membrane exhibited poorer mass transfer at low temperatures due to a decline in dense polymer permeability. Crucially in this study, neither wetting of the microporous membrane or plasticisation of the nonporous membrane were observed following pressurisation. Consequently, CO2 flux increased in proportion to the applied pressure for both membrane types, emphasising the critical role of pressurisation in augmenting process intensification for biogas upgrading which is typically facilitated at pressures of 7–10 bar. Resistance-in-series analysis illustrated how pressurisation reduced gas-phase resistance, and subsequently enhanced selectivity. Consequently, an outlet gas quality of 98% methane could be achieved within a single microporous module at 4.5 bar, meeting the industrial standard for biomethane whilst reducing solvent requirements, separation energy and methane losses. Comparable behaviour was observed during pressurisation of the nonporous membrane, but with a less significant benefit to CO2 mass transfer and selectivity, ostensibly due to the resistance imparted by the dense polymer. When considered collectively, low solvent temperature and high gas pressure enhance process intensification subsequently reducing process size (e.g., membrane area) and separation energy, while also advancing selectivity to deliver a gas product at the composition required for biomethane with minimum methane losses, which are critical factors in demonstrating microporous HFMC as an industrially competitive solution for biogas upgrading.